1. Technical Field of the Invention
The present invention relates generally to an improved structure of a push-button switch for use in electronic devices which achieves a long service life and operates with high reliability and confidence levels.
2. Background of Related Art
FIGS. 9 and 10 show a conventional push-button switch which includes generally a box-like resinous casing 1, a stationary contact 2, a holder 3, a cover 4, a button or knob 5, and a spring plate 6.
The stationary contact 2 and the holder 3 are secured on an inner bottom wall of the casing 1. The cover 4 is connected to the casing 1 in a snap fit of a claw 1A of the casing 1 into a hole 4B of the cover 4 and has an upper opening 4A through which the knob 5 slides vertically, as viewed in the drawing, when a knob head 5A is depressed downward.
The spring plate 6 includes a movable contact 6A, a supporting portion 6B, and a flexible strip 6C. The supporting portion 6B is secured in a recess 3A of the holder 3. The flexible strip 6C is held at its end in a recess 3B of the holder 3 to urge the movable contact 6A into constant engagement with the bottom of the knob 5.
In operation, when the knob head 5A is, as shown in FIG. 10, pushed down by a finger pressure of an operator, it will cause the spring plate 6 to be turned about a junction of the recess 3A and the support portion 6B into engagement of an end of the movable contact 6A with an end of the stationary contact 2, thereby establishing an electrical connection of the holder 3 and the stationary contact 2.
When the finger pressure is released from the knob head 5A, it will cause the flexible strip 6C of the spring plate 6 to be urged elastically upward to lift the knob 5 up to its initial position, thereby moving the movable contact 6A out of engagement with the stationary contact 2 to block the electrical connection of the holder 3 and the stationary contact 3.
The above conventional push-button switch, however, has the following drawback.
During the turning on and off operations of the push-button switch, the stress concentrates at a base of the flexible strip 6C of the spring plate 6, which leads to concern about breakage of the flexible strip 6C. An increase in rigidity of the flexible strip 6C of the spring plate 6 in order to avoid such a problem also leads to an increase in size of the spring plate 6, thus resulting in an increase in overall size and weight of the push-button switch.